The PET (Position Emission Tomography) is utilized as a method of diagnosing the diseased part by injecting a emission radioactive isotope into the body of a patient and measuring .alpha.-rays emitted from positron released from the isotope to determine the distribution of the radioactive isotope at each slice. As the synthesis of the radioactive isotope, for example, a synthesis of pyruvate-1-.sup.11 C is disclosed in Japanese Patent KOKAI No. 1-294639. In this method, .sup.11 CO.sub.2 is produced by a cyclotron, and the exchange reaction occurs between the .sup.11 CO.sub.2 and non-radioactive pyruvate. In the synthesis, syringes are utilized for the injection of NaOH, transfer of a substrate solution and the like, but it is not disclosed at all to check whether these reagent solutions are sufficiently sucked into the syringe or not.
As the producing technique of .sup.13 N-ammonia, it is known to use the apparatus shown in FIG. 7 (RADIOISOTOPES, vol. 30, pp 1-6, 1981). In the method of producing .sup.13 N-ammonia using the apparatus, a fixed amount of target water is charged into an irradiation cell 8 through a three way cock 27 and a two way cock 28. Subsequently, the cock 27 is changed over, the whole amount of the target water remaining in a liquid feed pipe 30 is put into the irradiation cell 8 by using pressurized helium gas or nitrogen gas as the carrier gas. At that time, the carrier gas is discharged from pipe 32 by opening cock 31. Then, cock 27, cock 28 and cock 31 are closed, and when proton beam is irradiated, oxygen atoms in the target water reacts to produce .sup.13 N through nuclear reaction. The nitrogen atoms react with surrounding oxygen atoms to produce .sup.13 N-nitrate ions (.sup.13 N--NO.sub.3.sup.-). Subsequently, the target water to which the irradiation is finished is put into reaction vessel 35 by opening cock 34 and then cock 27 and cock 28. Then, reagent TiCl.sub.3 in vial 38 is put into the reaction vessel 35 by opening cock 36 and cock 37. Reagent NaOH in vial 41 is further put into the reaction vessel 35 by opening cock 39 and cock 40. Subsequently, .sup.13 N-nitrate ions are allowed to react to be converted to .sup.13 -ammonia by heating the reaction vessel by heater 42. The ammonia is recovered into vial 45 through pipe 43 by distillation. In the past, .sup.13 N-ammonia was produced as stated above. Since water was also distilled and condensed in the vial 45, an isotonic liquid usable for injection was obtained by measuring the amount of the water therein and adding sodium chloride which was weighed according to the amount. It is not disclosed to utilize a syringe for the injection of liquid in the apparatus.
In the above producing method of .sup.13 N-ammonia, since .sup.13 N-nitrate ion is converted to .sup.13 N-ammonia, distilled and then purified it, a long time is necessary for obtaining it. Particularly, heating takes time due to distillation operation. As a result, more than 10 minutes are necessary from the end of the irradiation to taking out the produced .sup.13 N-ammonia into the vial 45. Since the half lifetime of .sup.13 N- is short, i.e. 9.96 minutes, about a half of .sup.13 N was lost by the decay in the meantime. Besides, since sodium chloride was weighed and added separately, it was also a problem that the operation was complex and troublesome and that the sodium chloride concentration was scattered.
Incidentally, as the means to charge a constant amount of a reagent solution or the like into a separate container automatically, there are the syringe method and the vial method. In the syringe method, a necessary amount of liquid is previously put in a syringe, and at the time of need, the piston of the syringe is depressed to charge it, and the method is disclosed in RADIOISOTOPE, vol. 33, pp 706-709, 1984, Eizo Joho (Image Information), 3, 1981, etc. In the vial method, a necessary amount of liquid is previously put in a vial, and at the time of need, the whole amount is delivered by pressurized He, N.sub.2, etc. gas, and the method is disclosed in Int. Appl. Radiat. Isot., vol. 36, No. 6, pp 469-474, 1985, ibid., vol. 35, No. 6, pp 445-454, 1984, etc.
In the syringe method, when liquid is sucked into the syringe, if there is clogging in the pipe, defective connection of the pipe, breakage of the pipe or the like, the sucked amount of the liquid into the syringe is short. In the conventional automatic synthesis apparatus, the procedure automatically proceeded to the next process even in such a case, and troubles occurred, because of lacking any checking function thereof. Furthermore, waiting for a certain period is necessary at the time of sucking the liquid into the syringe. Besides, even in the case of using the same liquid, vials or syrings as many as the number of using it must be set, irrespective of the vial method or the syringe method.
The present invention has been achieved in order to solve the above problems, and an object of the invention is to provide a method capable of synthesizing .sup.13 N-ammonia in a short time by lasy operations.
Another object of the invention is to provide a means capable of preventing troubles by checking whether the necessary amount of liquid has been sucked into the syringe or not.
A further object of the invention is to provide a means capable of preventing troubles by checking whether the necessary amount of liquid has been sucked into the syringe or not.
A further object of the invention is to provide a means capable of omitting the waiting time at the time of sucking into the syringe and operating in a short time. This invention is particularly effective in the case of using a radioactive isotope having a short half lifetime, such as .sup.13 N.